The invention relates to a transmitter-receiver communication system which uses an extended communication signal encoded according to a digital encoding standard and comprising dam that is covered by an error protection block code. Various systems are known that use such extended communication signal encoded according to a digital encoding standard, such as the Compact Disc standard for hifi audio, and the extended version thereof, CD-ROM, that offers a higher degree of error protection for sensitive data. At present, television signals also being standardized according to a bit-based format. Such standardization often evolves through extended contacts between various manufacturers, governments, public bodies, and others. Besides standards for consumer communications, standards for professional communications have come into existence as well. Generally, the format has user bits and control bits, but this is not a prerequisite. The term "extended" indicates that the system allows for communicating more information than the minimum, thereby allowing additional physical, logical, or notional channel capability. Physical means additional data, such that the user would experience a higher throughput. Logical means that additional data is transferred that borrows its relevance from the main data, such as a time indication that could be made accessible to the user or be used for enabling easier random access when the data is stored in a memory. Notional means that the functionality of the additional data is transparent to the user, such as when it would allow the system an improved functionality. Various other possibilities exist.
The data content of the user bits is unpredictable, but their prescribed minimum amount is given. As a result, their existence is taken for granted.
Often, the extension bits are used on a system level, to signal, at the receiver side certain general properties of the signal organization. Such properties, without any limitation in the following recitation, may relate to the coding format of the associated user information, additional user information that may be added to the main user information according to discretion, frame numbering or time indication, or information that is self-referencing to the control information proper.
When a new standard for a communication signal, supra, is first set up, various ones of the control bits are left undefined but kept in reserve for possible later definition. In addition, the need has emerged for error protection of the control bits or other extension bits against burst and/or random errors. By itself, error protection block codes are well known. With respect to protection of the extension bits, certain ones of which have been defined according to some standardization or assignation protocol, whereas others are not (yet) so defined, and, as a result, can from the level of the control be considered as dummy or spare bits, there are various different possibilities. A first possibility is to set all undefined bits equal to zero and to have an error correction scheme cover both defined and undefined bits. However, the inventor has recognized that this amounts to throwing away transfer and error protection capability of the channel. Another aspect is to allow for a variable error correcting code (ECC) strategy to cope with known channel quality variations, i.e., the decoder should be allowed to decide which level of error protection to be applied.